This invention generally relates to a switch mechanism for sensing the rotation of a shaft and, more particularly, to a safety switch mechanism employed in an escalator or power ramp to terminate operation thereof when an output shaft in the drive train reverses its rotation when the motor is driving the escalator or ramp upwardly. While the invention is particularly useful in conjunction with escalators or power ramps, it need not be so limited and may be employed in many fields.
Escalators and power ramps are specialized endless conveyors. Typically, a motor operates through a drive train including a gearbox to drive a main drive sprocket for the endless conveyor. Various controls are utilized to provide safety for passengers. These controls include a safety brake which automatically goes into operation when power to the motor is cut off. When an escalator is to be driven in the up direction, the motor control circuit is closed through a key-operated "up" switch, momentarily manually operated, which causes the motor to drive the escalator in an up mode until some protective safety switch operates, or until the escalator is turned off manually.
If the drive motor and the drive sprocket, which moves the conveyor, cannot move the conveyor and its load in the up direction, the conveyor can "freewheel" in the downward direction under the weight of the passengers upon it. It is therefore necessary in such circumstances to provide a means for opening the motor control circuit in order to set the brake and restrain downward movement of the conveyor.